A delayed sperm penetration of cumulus layers by disruption of acrosin gene in rats

Generation of rat-derived lung epithelial cells in Fgfr2b-deficient mice retains species-specific development

Regenerative medicine is a tool to compensate for the shortage of lungs for transplantation, but it remains difficult to construct a lung in vitro due to the complex three-dimensional structures and multiple cell types required. A blastocyst complementation method using interspecies chimeric animals has been attracting attention as a way to create complex organs in animals, although successful lung formation using interspecies chimeric animals has not yet been achieved. Here, we applied a reverse-blastocyst complementation method to clarify the conditions required to form lungs in an Fgfr2b-deficient mouse model. We then successfully formed a rat-derived lung in the mouse model by applying a tetraploid-based organ-complementation method. Importantly, rat lung epithelial cells retained their developmental timing even in the mouse body. These findings provide useful insights to overcome the barrier of species-specific developmental timing to generate functional lungs in interspecies chimeras.

Characterization of acrosin and acrosin binding protein as novel CRISP2 interacting proteins in boar spermatozoa

BACKGROUND

Previously, we reported that cysteine-rich secretory protein 2 is involved in high molecular weight complexes in boar spermatozoa. These cysteine-rich secretory protein 2protein complexes are formed at the last phase of sperm formation in the testis and play a role in sperm shaping and functioning.

OBJECTIVES

This study aimed to identify cysteine-rich secretory protein 2 interacting partners. These binding partner interactions were investigated under different conditions, namely, non-capacitating conditions, after the induction of in vitro sperm capacitation and subsequently during an ionophore A23187-induced acrosome reaction.

MATERIALS AND METHODS

The incubated pig sperm samples were subjected to protein extraction. Extracted proteins were subjected to blue native gel electrophoresis and native immunoblots. Immunoreactive gel bands were excised and subjected to liquid chromatography-mass spectrometry (LC-MS) analysis for protein identification. Protein extracts were also subjected to CRISP2 immunoprecipitation and analyzed by LC-MS for protein identification. The most prominent cystein-rich secretory protein 2 interacting proteins that appeared in both independent LC-MS analyses were studied with a functional in situ proximity interaction assay to validate their property to interact with cystein-rich secretory protein 2 in pig sperm.

RESULTS

Blue native gel electrophoresis and native immunoblots revealed that cystein-rich secretory protein 2 was present within a ∼150 kDa protein complex under all three conditions. Interrogation of cystein-rich secretory-protein 2-immunoreactive bands from blue native gels as well as cystein-rich secretory protein 2 immunoprecipitated products using mass spectrometry consistently revealed that, beyond cystein-rich secretory protein 2, acrosin and acrosin binding protein were among the most abundant interacting proteins and did interact under all three conditions. Co-immunoprecipitation and immunoblotting indicated that cystein-rich secretory protein 2 interacted with pro-acrosin (∼53 kDa) and Aacrosin binding protein under all three conditions and additionally to acrosin (∼35 kDa) after capacitation and the acrosome reaction. The colocalization of these interacting proteins with cystein-rich secretory protein 2 was assessed via in situ proximity ligation assays. The colocalization signal of cystein-rich secretory protein 2 and acrosin in the acrosome seemed dispersed after capacitation but was consistently present in the sperm tail under all conditions. The fluorescent foci of cystein-rich secretory protein 2 and acrsin binding protein colocalization appeared to be redistributed within the sperm head from the anterior acrosome to the post-acrosomal sheath region upon capacitation.

DISCUSSION AND CONCLUSION

These results suggest that CRISP2 may act as a scaffold for protein complex formation and dissociation to ensure the correct positioning of proteins required for the acrosome reaction and zona pellucida penetration.

The testis-, epididymis-, or seminal vesicle-enriched genes Aldoart2, Serpina16, Aoc1l3, and Pate14 are not essential for male fertility in mice

Spermatozoa released from the testis acquire fertilizing ability by translocating thorough the epididymis. Further, accessory gland secretions ejaculated into the female reproductive tract along with spermatozoa are also required to ensure male fecundity, such as the maintenance of proper sperm count and inhibition of premature sperm capacitation in the uterus. Here, we focus on a testis-enriched gene "Aldoart2", an epididymis-enriched gene "Serpina16", and seminal vesicle-enriched genes "Aoc1l3" and "Pate14" which were thought to be important for male fertility based on the previous studies. We independently deleted almost the entire protein-coding sequence of these genes in mice using CRISPR/Cas9. There were no overt defects in the histology and the sperm morphology and motility of any knockout (KO) mice. Further, Aoc1l3 and Pate14 KO males were able to form copulatory plugs. Finally, female mice that mated with these KO males delivered pups at a comparable level with the control males. Given our data, we demonstrated that the four genes predominantly expressed in the testis, epididymis, or seminal vesicle are independently dispensable for male fertility.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

In vitro effects of aqueous extract of unfermented rooibos on human spermatozoa

The inability to conceive is a baleful experience for thousands of couples worldwide. Among different well-known reproductive techniques, medicinal plants have been utilized to treat male infertility. Medicinal plants, provide a therapeutic alternative, which is available and affordable for infertile couples. We investigated the direct effect of unfermented rooibos aqueous extract on human spermatozoa. Semen samples (n = 50) collected from donors and patients consulting for fertility were reassigned as normal (n = 22) and abnormal (n = 28) samples based on the outcome of the baseline semen analysis, using the World Health Organization (WHO) cut off value. Semen samples were allowed to liquefy and subsequently washed with human tubular fluid in bovine serum albumin medium. The samples were then treated with aqueous extracts of unfermented rooibos (0, 0.15, 1.5, 15, 150 μg/ml) at 37°C for 1 h and assessed thereafter. Sperm motility, vitality, DNA fragmentation, intracellular reactive oxygen species and mitochondrial membrane potential in both groups remained unchanged (p > 0.05). However, aqueous extract of unfermented rooibos (only at 1.5 μg/ml) significantly increased capacitation and acrosome reaction in the abnormal sample group (p > 0.05). Unfermented rooibos aqueous extract had no deleterious impact on human spermatozoa's function and might be attributed to its antioxidant properties.

Recurrent Co-Option and Recombination of Cytokine and Three Finger Proteins in Multiple Reproductive Tissues Throughout Salamander Evolution

Reproductive proteins evolve at unparalleled rates, resulting in tremendous diversity of both molecular composition and biochemical function between gametes of different taxonomic clades. To date, the proteomic composition of amphibian gametes is largely a molecular mystery, particularly for Urodeles (salamanders and newts) for which few genomic-scale resources exist. In this study, we provide the first detailed molecular characterization of gametes from two salamander species (Plethodon shermani and Desmognathus ocoee) that are models of reproductive behavior. Long-read PacBio transcriptome sequencing of testis and ovary of both species revealed sex-specific expression of many genes common to vertebrate gametes, including a similar expression profile to the egg coat genes of Xenopus oocytes. In contrast to broad conservation of oocyte genes, major testis transcripts included paralogs of salamander-specific courtship pheromones (PRF, PMF, and SPF) that were confirmed as major sperm proteins by mass spectrometry proteomics. Sperm-specific paralogs of PMF and SPF are likely the most abundant secreted proteins in P. shermani and D. ocoee, respectively. In contrast, sperm PRF lacks a signal peptide and may be expressed in cytoplasm. PRF pheromone genes evolved independently multiple times by repeated gene duplication of sperm PRF genes with signal peptides recovered through recombination with PMF genes. Phylogenetic analysis of courtship pheromones and their sperm paralogs support that each protein family evolved for these two reproductive contexts at distinct evolutionary time points between 17 and 360 million years ago. Our combined phylogenetic, transcriptomic and proteomic analyses of plethodontid reproductive tissues support that the recurrent co-option and recombination of TFPs and cytokine-like proteins have been a novel driving force throughout salamander evolution and reproduction.

Sperm IZUMO1 Is Required for Binding Preceding Fusion With Oolemma in Mice and Rats

Fertilization occurs as the culmination of multi-step complex processes. First, mammalian spermatozoa undergo the acrosome reaction to become fusion-competent. Then, the acrosome-reacted spermatozoa penetrate the zona pellucida and adhere to and finally fuse with the egg plasma membrane. IZUMO1 is the first sperm protein proven to be essential for sperm-egg fusion in mammals, as Izumo1 knockout mouse spermatozoa adhere to but fail to fuse with the oolemma. However, the IZUMO1 function in other species remains largely unknown. Here, we generated Izumo1 knockout rats by CRISPR/Cas9 and found the male rats were infertile. Unlike in mice, Izumo1 knockout rat spermatozoa failed to bind to the oolemma. Further investigation revealed that the acrosome-intact sperm binding conceals a decreased number of the acrosome-reacted sperm bound to the oolemma in Izumo1 knockout mice. Of note, we could not see any apparent defects in the binding of the acrosome-reacted sperm to the oolemma in the mice lacking recently found fusion-indispensable genes, Fimp, Sof1, Spaca6, or Tmem95. Collectively, our data suggest that IZUMO1 is required for the sperm-oolemma binding prior to fusion at least in rat.

Quercetin-treated rat sperm enables refrigerated transport with motility and fertility for five days

Shipment of laboratory rats between animal facilities is frequently performed using special containers. However, the shipment of live animals is associated with potential risks of infectious diseases, escape and death during shipment and animal welfare issues. The transport of cold-stored sperm avoids such risks; however, there have been no reports on cold storage of rat sperm. We previously reported that dimethyl sulfoxide (DMSO) and quercetin maintained the motility and fertilising abilities of cold-stored mouse sperm stored for 10 days. The present study investigated the efficacy of DMSO and quercetin in the cold storage of rat sperm. Quercetin maintained motility and fertility of cold-stored rat sperm stored for 5 days. After in vitro fertilisation using cold-stored sperm, pronuclear and two-cell embryos developed normally to pups following embryo transfer. Therefore, we demonstrated that live pups could be obtained from sperm transported using the cold-storage system. We conclude that cold storage of rat sperm may provide an efficient system for transporting rat resources as an alternative to shipping live animals.

Ligands and Receptors Involved in the Sperm-Zona Pellucida Interactions in Mammals

Sperm-zona pellucida (ZP) interaction, involving the binding of sperm surface ligands to complementary carbohydrates of ZP, is the first direct gamete contact event crucial for subsequent gamete fusion and successful fertilization in mammals. It is a complex process mediated by the coordinated engagement of multiple ZP receptors forming high-molecular-weight (HMW) protein complexes at the acrosomal region of the sperm surface. The present article aims to review the current understanding of sperm-ZP binding in the four most studied mammalian models, i.e., murine, porcine, bovine, and human, and summarizes the candidate ZP receptors with established ZP affinity, including their origins and the mechanisms of ZP binding. Further, it compares and contrasts the ZP structure and carbohydrate composition in the aforementioned model organisms. The comprehensive understanding of sperm-ZP interaction mechanisms is critical for the diagnosis of infertility and thus becomes an integral part of assisted reproductive therapies/technologies.

Seeing is believing: Current methods to observe sperm acrosomal exocytosis in real time

Acrosomal exocytosis (AR) is a critical process that sperm need to undergo to fertilize an egg. The evaluation of the presence or absence of the acrosome is usually performed by using lectins or dyes in fixed cells. With this approach, it is neither possible to monitor the dynamic process of exocytosis and related molecular events while discriminating between live and dead cells, nor to evaluate the acrosomal status while sperm reside in the female reproductive tract. However, over the last two decades, several new methodologies have been used to assess the occurrence of AR in living cells allowing different groups to obtain information that was not possible in the past. These techniques have revolutionized the whole study of this process. This review summarizes current methods available to analyze AR in living cells as well as the important information that emerged from studies using these approaches.

Green tea consumption increases sperm concentration and viability in male rats and is safe for reproductive, liver and kidney health

Green tea is a popularly consumed beverage worldwide and contains polyphenols, whose antioxidant activities could improve sperm parameters and fertility thereof. We investigated the effect of green tea on the male rat reproductive system as well as its safety. Male Wistar rats were administered 2 and 5% aqueous extract of green tea for 52 days’ ad libitum, while the control group received tap water. Total polyphenol, flavanol, flavonol and soluble solids significantly increased in a concentration-dependent manner in vitro (P < 0.01). Weights of body, testis, epididymis, prostate gland, seminal vesicles, and liver, serum levels of testosterone, ferric reducing antioxidant power, creatinine, and sperm motility, remained unchanged (P > 0.05). Kidney weight, sperm concentration and vitality, spontaneous acrosome reaction increased (P < 0.05), while alanine transaminase and aspartate transaminase levels decreased (P < 0.05). Catalase, superoxide dismutase, glutathione and lipid peroxidation remained unchanged in the testes, liver and kidney (P > 0.05). Histological sections of testis, epididymis, kidney and liver showed no conspicuous alteration. Diameter and epithelial height of seminiferous tubule decreased, while caudal epididymis epithelial height increased (P < 0.01). Consumption of green tea in the conditions used in the present study seems to be safe and improved sperm parameters. However, subtle structural changes observed in the decreased diameter and epithelial height of the seminiferous tubule and increased acrosome reaction needs further investigation.

Boar spermatozoa proteomic profile varies in sperm collected during the summer and winter

Boar sperm quality is less during the summer as a result of the different photoperiod or ambient temperatures as compared with the winter. The present study was conducted to elucidate possible variations in proteomic profiles of boar spermatozoa collected during the summer and winter. Effects of season on sperm viability, total motility, progressive motility, acrosome status, mitochondrial membrane potential and plasma membrane lipid organization were also analyzed. Only sperm viability and mitochondrial membrane potential were less during the summer (P <  0.05). Spermatozoa were processed and evaluated using the nano LC-MS/MS QTof procedures. A total of 1028 characterized proteins were identified in sperm collected during both seasons of the year (False Discovery Rate < 0.01) and, among the total, 85 proteins differed in sperm collected in the winter and summer, with there being a lesser abundance of these proteins when there were ejaculate collections during the summer (q-value ≤ 0.05). The results from enrichment assessments for these protein networks utilizing UniProtKB procedures for determining reproductive processes indicates there were 23 proteins that were less abundant in the summer than winter. These proteins have essential functions in spermatogenesis, sperm motility, acrosome reaction and fertilization. These results are the first where there was ascertaining of proteomic differences in boar spermatozoa collected in the summer and winter. These results might help to explain the decreased sperm quality and prolificity when semen of boars is used for artificial insemination that is collected during the season of the year when ambient temperatures are relatively greater.

Preventing polyspermy in mammalian eggs-Contributions of the membrane block and other mechanisms

The egg's blocks to polyspermy (fertilization of an egg by more than one sperm) were originally identified in marine and aquatic species with external fertilization, but polyspermy matters in mammalian reproduction too. Embryonic triploidy is a noteworthy event associated with pregnancy complications and loss. Polyspermy is a major cause of triploidy with up to 80% of triploid conceptuses being the result of dispermic fertilization. The mammalian female reproductive tract regulates the number of sperm that reach the site of fertilization, but mammals also utilize egg-based blocks to polyspermy. The egg-based blocks occur on the mammalian egg coat (the zona pellucida) and the egg plasma membrane, with apparent variation between different mammalian species regarding the extent to which one or both are used. The zona pellucida block to polyspermy has some similarities to the slow block in water-dwelling species, but the mammalian membrane block to polyspermy differs substantially from the fast electrical block that has been characterized in marine and aquatic species. This review discusses what is known about the incidence of polyspermy in mammals and about the mammalian membrane block to polyspermy, as well as notes some lesser-characterized potential mechanisms contributing to polyspermy prevention in mammals.

In vivo effects of black tea on the male rat reproductive system and functions of the kidney and liver

This study focused on the effects of black tea on the male reproductive system as well as the kidney and liver functions. Male Wistar rats were given aqueous extract of black tea (2% and 5%) for 52 days as the only means of drinking fluid, while control rats received tap water. Black tea enhanced sperm vitality (44%-49%), total sperm motility (10%-12%) and acrosome reaction (2%-9%) (p < .05). Body weight gain, testis, epididymis, seminal vesicles, prostate, liver weight, testosterone level, sperm concentration, ferric reducing antioxidant power (FRAP) and antioxidant levels in the testes, liver and kidney remained unchanged (p > .05). Black tea (5%) increased kidney weight (p < .05). Testis and epididymis showed normal histological appearance. However, black tea significantly reduced the diameter (9%-10%) and epithelial height (9%-10%) of the seminiferous tubule, but increased the epithelial height of the cauda epididymis (8%-24%) (p < .05). A significant reduction in serum levels of alanine aminotransaminase (ALT) (38%) and aspartate aminotransaminase (AST) (23%-34%) was observed (p < .05); creatinine level, on the other hand, increased (8%-72%) (p < .05). Black tea improved several sperm parameters, but may cause subtle changes in certain reproductive organs and the kidney functions.

Lycium barbarum polysaccharide protects against ethanol-induced spermiotoxicity and testicular degeneration in Immp2l+/- mice

Studies have indicated that high levels of ethanol exposure impaired spermatogenesis in mice. However, the effects of chronic and low-dose alcohol consumption on susceptible populations remain unclear. The previous studies have confirmed that Immp2l mutant mice (Immp2l^{Tg(Tyr)979Ove} or Immp2l^-/- ) suffered from increased levels of oxidative stress(OS) and male infertility, heterozygous lmmp2l mice (Immp2l^+/- ) showed no altered ROS levels under physiological condition. Lycium barbarum polysaccharide (LBP) significantly scavenge oxygen free radicals and enhance antioxidant enzyme activity. The objectives of present study were to research the effects of chronic and low-dose alcohol-induced damage on Immp2l^+/- , explore the protective function of LBP and possible mechanism. The results indicated that chronic ethanol exposure leads to spermatogenic impairment and triggered a toxic effect on germ cell, 10 mg/kg LBP administration improved the quality of spermatozoon, decreased the ratio of apoptotic germ cells and the expression of Col1a1 and Col1a2, while increased the level of TNP2 and RPL31. In conclusion, the study may provide basic knowledge about LBP's important role against ethanol-induced spermiotoxicity and testicular degeneration in Immp2l^+/- mice, and the mechanism may be that LBP influenced the state of the spermatogenic epithelium by decreasing the expression of Collagen level leading to alterations in protein biosynthesis during the process of spermatogenesis.

Acrosin is essential for sperm penetration through the zona pellucida in hamsters

During natural fertilization, mammalian spermatozoa must pass through the zona pellucida before reaching the plasma membrane of the oocyte. It is assumed that this step involves partial lysis of the zona by sperm acrosomal enzymes, but there has been no unequivocal evidence to support this view. Here we present evidence that acrosin, an acrosomal serine protease, plays an essential role in sperm penetration of the zona. We generated acrosin-knockout (KO) hamsters, using an in vivo transfection CRISPR/Cas9 system. Homozygous mutant males were completely sterile. Acrosin-KO spermatozoa ascended the female genital tract and reached ovulated oocytes in the oviduct ampulla, but never fertilized them. In vitro fertilization (IVF) experiments revealed that mutant spermatozoa attached to the zona, but failed to penetrate it. When the zona pellucida was removed before IVF, all oocytes were fertilized. This indicates that in hamsters, acrosin plays an indispensable role in allowing fertilizing spermatozoa to penetrate the zona. This study also suggests that the KO hamster system would be a useful model for identifying new gene functions or analyzing human and animal disorders because of its technical facility and reproducibility.

Sperm-egg interaction and fertilization: past, present, and future

Fifty years have passed since the findings of capacitation and acrosome reaction. These discoveries and the extensive effort of researchers led to the success of in vitro fertilization, which has become a top choice for patients at infertility clinics today. The effort to understand the mechanism of fertilization is ongoing, but the small number of eggs and similarly small quantity of spermatozoa continue to hinder biochemical experiments. The emergence of transgenic animals and gene disruption techniques has had a significant effect on fertilization research. Factors considered important in the early years were shown not to be essential and were replaced by newly found proteins. However, there is much about sperm-egg interaction which remains to be learned before we can outline the mechanism of fertilization. In fact, our understanding of sperm-egg interaction is entering a new stage. Progress in transgenic spermatozoa helped us to observe the behavior of spermatozoa in vivo and/or at the moment of sperm-egg fusion. These advancements are discussed together with the paradigm-shifting research in related fields to help us picture the direction which fertilization research may take in the future.

Fluoride Interferes with the Sperm Fertilizing Ability via Downregulated SPAM1, ACR, and PRSS21 Expression in Rat Epididymis

Fluoride is a widespread environmental pollutant that can induce low sperm quality and fertilizing ability; however, the underlying mechanism still remains unclear. Hence, we aimed to investigate the influence of fluoride on the sperm fertilizing ability via some key proteins in the epididymis. For this, 40 adult rats were assigned randomly into four groups. The control group was given distilled water, while the other three groups were given 25, 50, and 100 mg of NaF/L via drinking water for 56 days, respectively. After 1 day, epididymides were processed for sperm-egg binding, RNA extraction, western blot, and immunofluorescence analysis. Fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer. A further study revealed that fluoride altered the expression levels of genes and proteins related to acrosome reaction in vivo, including SPAM1, ACR, and PRSS21. However, fluoride only affected the expression of the ACR protein only in the epididymis but not in the testis. Fluoride also affected the expression levels of the membrane proteins CD9 and CD81 of epididymosomes in the epididymis. From the results, it can be concluded that fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer, which could be one of the reasons for decreased fertility ability in males treated with fluoride. These results provide some theoretical guidance and new ideas for treatments of low fertility, infertility, and other reproductive diseases.

The golden (Syrian) hamster as a model for the study of reproductive biology: Past, present, and future

BACKGROUND

The golden (Syrian) hamster (Mesocricetus auratus) is a small rodent that belongs to the Cricetidae family. It has several unique features that are advantageous for the study of reproductive and developmental biology, including a consistent estrous cycle (4 days), high responsiveness to conventional superovulation regimens, and the short gestation period (16 days).

METHODS

Based on the published reports, the development in assisted reproductive technology (ART) in the golden hamsters was summarized.

MAIN FINDINGS

The technical ease of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in this species has contributed to our understanding of the basic mechanisms of mammalian fertilization in the last century. However, a strong developmental block in vitro of hamster embryos and unavailability of gene-modified strains has hampered its broader use in biomedical fields. A recently developed in vivo transfection method has enabled us to generate gene knockout hamsters without any major obstacles. It would be interesting to revisit the genes whose functions could not be identified using mouse models.

CONCLUSION

The authors expect that gene knockout hamsters might be able to substitute for mice-at least in part-for better understanding of gene functions in mammals including humans.

The serine protease testisin is present on the surface of capacitated stallion spermatozoa and interacts with key zona pellucida binding proteins

BACKGROUND AND OBJECTIVES

Serine proteases are emerging as important players in the spermatozoon's acquisition of functional competence. This study aimed to characterize the serine protease testisin (PRSS21) in stallion spermatozoa, examining its surface expression, possible origins in the testis and epididymis, and changes in response to capacitation and acrosome reaction, as well as its capacity to form high molecular weight complexes and interact with other proteins.

MATERIALS AND METHODS

The role of serine proteases in spontaneous capacitation and acrosome reaction of stallion spermatozoa was established using the serine protease inhibitor, AEBSF. Testisin localization, before and after exposure of stallion spermatozoa to capacitating conditions and calcium ionophore, was examined using live cell immunofluorescence and flow cytometry. Immunohistochemistry of testicular and epididymal tissues was used to further dissect the origins of sperm testisin. Testisin's participation in high molecular weight protein complexes and identification of its interacting partner proteins were investigated using Blue Native PAGE, co-immunoprecipitation, and mass spectrometry, with interrogation of protein-protein interaction databases and gene ontology analysis of partner proteins used to further explore the potential roles of the testisin-containing complex in sperm function.

RESULTS

Testisin surface expression increased significantly in capacitated spermatozoa (p < 0.001), increased further following acrosome reaction (p < 0.01), and was localized to the equatorial region of the sperm head. Testisin was also detected in luminal fluid within the caput and corpus regions of the epididymis, epididymal spermatozoa, and epididymal epithelial cells. Testisin formed several multiprotein complexes; co-immunoprecipitation revealed interactions of testisin with a multitude of zona pellucida-binding proteins, including ZPBP, ZAN, acrosin, several heat-shock proteins, and components of the TCP1 complex.

CONCLUSION

Testisin appears to form part of the zona pellucida-binding complex in stallion spermatozoa and may be involved in the proteolytic cascade that prepares the sperm surface for interaction with the oocyte.